<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>

        .father {
            width: 200px;
            height: 200px;
            background-color: aqua;
        }

        /* 这个content的css属性值必须要有，否则会失效 */

        .father::before{
            content: 'hello，';
            color:khaki;
        }
        .father::after {
            content: "欢迎来我的世界！";
            color: bisque;
        }

    </style>
</head>
<body>

    <div class="father">
        smile-frank
    </div>    
</body>
</html>